Uptake of Evans blue-bound albumin in the aorta of oestrogen-treated rats.

The permeability of the aortic endothelium was studied in oophorectomized female rats following i.m. administration of ethinyloestradiol daily for 10 days. For this purpose a solution of Evans blue: albumin (1%:5%) in Ringer's solution was perfused under controlled pressure through the left ventricle. Areas of blue staining, seen through the intimal surface, were taken to indicate areas of endothelial permeability to albumin. They were traced within the outline of the intimal surface of the whole vessel. The total stained area, expressed as a percentage of the total area of the intimal surface, was determined separately for the various segments in both the thoracic and abdominal aortas. Statistical analysis of data indicated that the uptake of Evans blue-bound albumin in the aortic wall was significantly increased in oestrogen-treated rats as compared to their control. This phenomenon was observed throughout the aorta except for its middle abdominal segment. Also its magnitude was comparable in all segments. These results strongly suggest that endothelial permeability to albumin was increased following treatment with synthetic oestrogen. This would enhance the influex of growth-promoting factors and thus play a role in the pathogenesis of proliferative lesions in the arterial wall associated with oestrogen administration in humans as well as in experimental animals.